One of the drawbacks of being subbed to lots of comms in several different instances: dupe posts. There’s no central method to detect them, and not everyone is subbed to the same instances, so not everyone would see them all anyway.

The crosspost feature helps, but it only works if all of the posts are made by the same user or shared from the original post.

No. At least not in this community. If you follow multiple news communities on Lemmy then you’re going to get some overlap, of course.

No idea. I don’t see anything about it on the first page.